1. Field of the Invention
The present invention relates to an apparatus for restoring an ink jet recording head for use in an ink jet printer in which ink is ejected to a recording sheet from an ejecting nozzle to perform recording and an ink jet printer provided with the apparatus. More specifically, the present invention relates to a preferable apparatus for restoring an ink jet recording head for restoring the condition of ink non-ejection which is caused by the adhesion of foreign particles to the nozzle face or the occurrence of air bubbles in an ejecting nozzle, and an ink jet printer provided with the apparatus.
2. Description of the Related Art
In general, an ink jet printer is used as an output device of a computer, a word processor, or the like.
In a conventional ink jet printer, a carriage shaft is disposed in a direction parallel with a flat platen, and a reciprocatable carriage is disposed along the carriage shaft. Moreover, an ink jet recording head is mounted on the carriage to oppose to the platen in such a manner that a head nozzle of the ink jet head faces a printing face of the platen.
According to the above conventional ink jet printer, a recording sheet is conveyed between the platen and the ink jet head. While the carriage having the ink jet head mounted thereon moves along the platen, the nozzle of the ink jet head is operated on the basis of a predetermined printing signal, so that the desired ink is ejected or discharged from the nozzle toward the recording sheet on the platen. Thus, a desired image is recorded or printed on the recording sheet.
When such ink jet printer is used to perform recording, there is a case in which foreign particles adhere onto a nozzle face or air bubbles are mixed into or generated in the ink passage of the ejecting nozzle of the ink jet recording head. The sticking foreign particles or air bubbles clog or narrow a nozzle port of the ejecting nozzle, which causes ink non-ejection.
To solve the ink non-ejection problem, in the conventional ink jet printer, the foreign particles or bubbles are removed from the ejecting nozzle by a restoring apparatus. A suction method and a pressurizing method are known as restoring methods. In the suction method, an ink jet recording head is moved to a home position of a carriage, a cap is attached to and covers an ejecting nozzle, and suction is performed to make negative a pressure in the cap, so that the foreign particles are sucked together with ink from the ejecting nozzle to restore the non-ejectable condition. In the pressurizing method, the foreign particles are ejected or discharged together with the ink from the ejecting nozzle by pressurizing the ink in an ink tank, to restore the non-ejectable condition of the ink jet head.
In the suction method, in order to suck the ink by the cap, the ejecting nozzle needs to be hermetically sealed by contacting the cap closely to the ejecting nozzle, but it is difficult to keep hermetic the inside of the cap. Moreover, in the conventional pressurizing method, it is difficult to keep constant an ink ejecting pressure of each ejecting nozzle for restoration, and a dispersion of the ink ejecting pressure often happens. If an excessive inner pressure acts inside the normal ejecting nozzle, unnecessary and undesired air bubbles may be generated in the normal ink jet recording head.
The present invention has been accomplished in consideration of the aforementioned circumstances, and a first object of the present invention is to provide an apparatus for restoring an ink jet recording head which can securely recover the ink jet recording head from the ink non-ejection condition caused by foreign particles or air bubbles adhering inside an ink passage and which can prevent unnecessary air bubbles from generating inside the ink passage of the ink jet recording head. A second object is to provide an ink jet printer provided with the apparatus.
According to the present invention, the first object can be attained by adjusting to a set pressure value an inner pressure of an ink supply passage increased by operating pressurizing means. Specifically, the object is attained by the provision of an apparatus for restoring an ink jet recording head which performs image recording by ejecting ink droplets to a recording sheet from an ejecting nozzle of the ink jet recording head, comprising:
non-ejection detecting means for detecting the occurrence of non-ejection of the ink drops from the ejecting nozzle to output a non-ejection signal;
pressurizing means for increasing an inner pressure of an ink supply passage connected to said ink jet recording head;
pressure measuring means for detecting the inner pressure of said ink supply passage; and
control means for controlling said pressurizing means based on said non-ejection signal in such a manner that the inner pressure of the ink supply passage detected by said pressure measuring means reaches a set pressure value to eject ink.
Here, a piezoelectric ink jet system can be applied to the ink jet head. In the system, a piezoelectric element is provided to contact the ink supply passage. By applying a drive voltage, the piezoelectric element is deformed to increase the inner pressure of the ink supply passage, and ink within the ink supply passage is ejected from the nozzle. The non-ejection detecting means can use the piezoelectric element for use in the piezoelectric ink jet system. Specifically, when the piezoelectric element is deformed by a change of the inner pressure of the ink supply passage, voltage is generated between its both ends (piezoelectric effect). Therefore, an ejection/non-ejection condition can be determined by monitoring the voltage generated by the piezoelectric effect. Here, immediately after the ink is normally ejected, the inner pressure of the ink supply passage is largely varied by movement of the ink. When no ink is ejected, however, no ink moves in the ink supply passage, and the variation of the inner pressure is reduced. When the voltage generated by the piezoelectric effect of the piezoelectric element is largely varied, it can be determined that ejection is normally performed. When the variation is reduced, non-ejection can be determined.
For the control means, when the non-ejection detecting means detects the ink non-ejection to output the non-ejection signal, the inner pressure of the ink supply passage is increased to a preset pressure value, and the piezoelectric element is then actuated, so that the ink is ejected from the ejecting nozzle. The foreign particles or air bubbles can thus securely be removed from the ink supply passage. In this case, when the drive voltage of the piezoelectric element is set to a voltage higher than the drive voltage at the time of normal operation, e.g., about twice the normal drive voltage, the ink ejecting pressure is further raised, and the foreign particles or air bubbles can be removed more securely.
In the restoring operation, it can simultaneously be judged whether or not the amount of ink remaining in the ink supply passage is lacking; i.e., whether or not there is remaining ink. In general, a pressure decreasing rate in a stationary state of the ink supply passage after once pressurized is relatively small, when a sufficient amount of ink remains in the ink supply passage. In contrast, the pressure decreasing rate is relatively large, when a lesser amount of the ink remains in the ink supply passage. The presence of remaining ink is determined by using the pressure decreasing rate which is changed by the remaining amount of ink. More specifically, in the restoring operation, after the ink supply passage is pressurized up to the predetermined pressure value, the piezoelectric element is actuated for a short time to discharge the foreign particles or bubbles. Additionally, during and after the operation of the piezoelectric element, the pressure decreasing rate is monitored. When the pressure decreasing rate is more than a predetermined rate, or when the pressure in the ink supply passage decreases to be less than a predetermined pressure, it is judged that there is no remaining ink.
The ink jet recording head may be provided with a buffering chamber for separating the air bubbles mixed into the ink. In order to adjust the amount of air accumulated in the buffering chamber with a head solenoid valve, the air amount adjustment of the buffering chamber may be performed prior to the restoring operation. Because there are cases in which, when the amount of air accumulated in the buffering chamber is equal to or more than a specified value, the air bubbles mixed into the ink cannot be separated, and non-ejection is caused. Therefore, in this case, after the ink supply passage is once pressurized in response to the non-ejection signal, and the head solenoid valve is opened to exhaust unnecessary air from the buffering chamber, the ink supply passage is again pressurized to perform the original restoring operation.
After the restoring operation, a nozzle face or tip end of the ejecting nozzle of the ink jet recording head may be cleaned with a wiper. In the ordinary restoring operation, after the ink supply passage is pressurized to eject the ink via the ejecting nozzle, the inner pressure of the ink supply passage is lowered. In this case, the ink droplets adhere to or remain in the tip end of the ejecting nozzle. Moreover, the ink or the foreign particles may adhere to a periphery of the nozzle port of the ejecting nozzle. The wiper for removing the ink or foreign particles from the ejecting nozzle can be operated during a time for releasing the inner pressure of the ink supply passage, after the restoring operation is completed.
The pressurizing means may be constituted by a pressurizing pump or air pump for supplying pressurizing air to the ink tank. In this case, the pressure measuring means may be formed by a pressure sensor for detecting an air pressure in a pressurizing air channel connecting the pressurizing pump and the ink tank.
When a plurality of ink jet recording heads and ink tanks are arranged for different colors, there are provided a pressure junction section which is pressurized by one pressurizing pump, and one pressure sensor and one pressure release valve connected to the pressure junction section. The pressure junction section may be separately connected to the tanks via tank solenoid valves. In this case, when the pressure junction section is maintained at a constant pressure, the constant pressure can be fed to an arbitrary ink tank by opening the associated tank solenoid valve. Therefore, different from a case in which the ink tanks are separately provided with pressurizing pumps, pressure sensors and pressure release valves, the structure can be simplified.
When there are provided a plurality of ink jet recording heads, each ink jet recording head is detected for the ink non-ejection condition, and the restoring operation can be applied only to the non-ejecting ink jet recording head. In this case, wasteful consumption of ink is minimized.
For the control means, after the inner pressure of the ink supply passage raised by operating the pressurizing means is once lowered, the inner pressure of the ink supply passage may be raised to the set pressure value again by operating the pressurizing means. In this case, the inner pressure of the ink jet recording head can easily and securely be raised to the set pressure value only by performing pressurizing in two stages.
According to the present invention, the second object can be attained by an ink jet printer in which ink is supplied to an ink jet recording head from an ink tank, and ejected to a recording sheet via an ejecting nozzle based on a predetermined recording signal to perform recording, comprising the aforementioned apparatus for restoring the ink jet recording head.